Calendrical software
Some calendars are sufficiently simple that their use requires no more calculation than can be done mentally. An example is the Gregorian Calendar, whose use requires nothing more complicated arithmetically than division of a year number by 400 (even though the rule for leap years is sufficiently complex that many people cannot understand it without mental effort). To determine the structure (of years, months, days, etc.) of a calendar it may be necessary to use complex calculations. An example is the Chinese Lunar Calendar, which requires an exact determination of the time of the dark moon at a particular longitude. The Chinese Calendar was invented over 2000 years ago, long before there were any computers in the modern sense of the term, so clearly a computationally intensive calendar can be developed and used without reliance on modern computers. But these days computation is indispensible in the study of calendars. This computation is of two kinds: That required simply to compute the structure of a calendar, and that required for more scholarly studies (for example, the extent to which new years day in a solar calendar varies with respect to one of the seasonal markers, in particular, the vernal equinox. This article discusses calendrical software of the first kind only. The obvious way to classify calendrical software of this kind is in terms of the calendars that it deals with. Some software, of course, handles dates in more than one calendar, so in what follows there is some duplication. In each of the calendars listed a distinction is made between software which is written for the PC, the Macintosh, some other system, or whether the software is a web application. Some of this software is free and some is try-before-you-buy (the name of the software publisher is given after the title). There are a couple of additional sections not concerned with specific calendars, such as software for calculating the dates of solstices and equinoxes. Annus Novus Decimal Calendar Windows software *Annus Novus Decimal Calendar Converter Hermetic Systems Arithmetic Operations on Calendar Dates The basic operations are the addition or subtraction of a number of days to or from a date, and the subtraction of one date from another (resulting in the number of days between two dates). Some software allows the option of includeing or excluding the first date, and of excluding weekend days from the calculations. Windows software *Easy Date Converter Hermetic Systems (The Advanced Version supports batch processing and custom date-processing scripts.] Web applications *Calculate duration between two dates Steffen Thorsen Armenian Calendar DOS (Windows console applications) *COMPUTUS Calendar conversion program Gerhard Behrens Aztec Calendar Web applications *Aztec Calendar Converter René Voorburg, William Horden and Marta Ramirez ' Bahai Calendar '''Web applications' *Yet Another Calender Converter Tim Forsythe ' Chinese Lunar Calendar '''Web applications' *Western-Chinese Calendar Converter Erik Peterson (Serverscript) *Western-Chinese Calendar Converter Erik Peterson (Java applet; doesn't work with Firefox) *Calendrica Edward M. Reingold Common Era Calendar (Gregorian Calendar) All (or almost all) calendar software intended for users in the West convert dates in some calendar to or from CE dates. Only the following kinds of software might be expected not to support conversion of CE dates: (a) Software intended for local use in a non-Western society. (b) Software for machine control lacking any way for humans to interact with it. Coptic Calendar Web applications *Conversion of Coptic and Julian dates J. Thomann /Institute of Oriental Studies at Zurich University DOS (Windows console applications) *COMPUTUS Calendar conversion program Gerhard Behrens Dee-Cecil Calendar Web applications *Yet Another Calender Converter Tim Forsythe Easter date Web applications *Easter Sunday/Jewish Passover Calculator Robert H. van Gent DOS (Windows console applications) *COMPUTUS Calendar conversion program Gerhard Behrens French Revolutionary Calendar Web applications *Yet Another Calender Converter Tim Forsythe Goddess Lunar Calendar DOS (Windows console applications) *Lunar Calendars and Eclipse Finder Hermetic Systems Hebrew Calendar Web applications *Calendar Converter John Walker *JOS Calendar Conversion Bernard Israelite Kouchel & Michael Tobias *The Calendar Converter Rafi Stern *Yet Another Calender Converter Tim Forsythe *Rosetta Calendar Scott E. Lee DOS (Windows console applications) *COMPUTUS Calendar conversion program Gerhard Behrens Hermetic Leap Week Calendar Hermetic Lunar Week Calendar The Hermetic Lunar Week Calendar specifies days by means of dates of the form year-month-week-day, where a year has 12 or 13 months, a month has exactly four weeks, and a week consists usually of 7 or 8 days but sometimes of 6 or 9 days. Weeks track the lunar quarters exactly. Windows software *Lunar Calendars and Eclipse Finder Hermetic Systems Web applications *Printable Hermetic Lunar Week Calendar Hermetic Systems *Hermetic Lunar Week Calendar Day Count Hermetic Systems Icelandic Calendar Web applications *Applet “Old Icelandic Calendar” Tim Stridmann Indian Civil Calendar Web applications *Yet Another Calender Converter Tim Forsythe Islamic (Hijri) Calendar Windows software *Accurate Times Mohammad Odeh (Lunar crescent sighting) Web applications *Calendar Converter John Walker *Yet Another Calender Converter Tim Forsythe *Conversion of Islamic and Christian dates J. Thomann /Institute of Oriental Studies at Zurich University DOS (Windows console applications) *Moon Calculator Monzur Ahmed (Lunar crescent sighting) ISO Week Calendar The ISO Week Calendar is a leap week calendar that is used mainly in government and business for fiscal years. It uses the conventional 7-day week, with weeks starting on Monday. Years begin within 3 days of the start of the Common Era Calendar year, and each year has exactly 52 or 53 weeks. There is not a lot of off-the-shelf software for conversion of dates in the ISO Week Calendar. Windows software *Easy Date Converter Hermetic Systems Web applications *The ISO Week Date Calendar Rick McCarty *Yet Another Calender Converter Tim Forsythe *calendar conversion Tadayoshi Funaba Japanese Calendar Web applications *calendar conversion Tadayoshi Funaba Julian Calendar Web applications *Calendar Converter John Walker *Yet Another Calender Converter Tim Forsythe *Rosetta Calendar Scott E. Lee Julian Day Number The Julian day number system is not itself a calendar, but is of central importance in the study of calendars. This system sets up a one-to-one correspondence between days (more exactly nychthemerons) as observed on Earth and the integers: ..., -2, -1, 0, 1, 2, 3 ... This allows identification of a particular day without reference to any particular calendar. An informal definition of the Julian day number is: The number of days elapsed since ‑4712-01-01 JC, that is, since January 1st, 4713 BCE in the Julian Calendar. It can also be defined as: The integral part of the astronomical Julian date at 12 noon GMT on that day. For example, the Julian day number of 2007-02-23 CE is 2,454,155. The software listed below supports conversion of dates in various calendars to and from Julian day numbers. Windows software *Chinese Calendrics Hermetic Systems *Easy Date Converter Hermetic Systems *Julian Day Converter Gedesoft *Lunar Calendars and Eclipse Finder Hermetic Systems *Mayan Calendrics Hermetic Systems *Trayday MJMSoft Design Web applications *Monthly Calendar & Julian Date Calculator 1728 Software Systems *Calendar Converter John Walker *Yet Another Calender Converter Tim Forsythe Kalacakra Calendar The Kalacakra Calendar is a lunisolar calendar in which days are numbered according to the Moon's longitude. DOS (Windows console applications) *Kalacakra Calendar Software Edward Henning Liberalia Triday Calendar The Liberalia Triday Calendar combines a solar calendar with a lunar calendar which have 'tridays' (periods of 3 days) in common. The Solar Liberalia Triday Calendar divides years into four quarters and the Lunar Liberalia Triday Calendar divides years into twelve months. Windows software *Lunar Calendars and Eclipse Finder Hermetic Systems Lunar and Solar Eclipses Windows software *Alcyone Ephemeris Alcyone Software Web applications *Sky View Cafe Kerry Shetline DOS (Windows console applications) *Calendars and Eclipse Finder Hermetic Systems Maya Calendar The Maya used three different calendrical systems (and some variations within the systems). The three systems are known as the tzolkin, the haab and the long count. The tzolkin is a cycle of 260 days and the haab is a cycle of 365 days. Since the Maya calendar is fairly complex, the need for software to handle dates in this calendar has long been recognized. Note that there is still some uncertainty regarding how dates in the Maya Calendar should be correlated with dates in the Common Era Calendar (this is known as the correlation problem). Thus all Maya Calendar software which converts Maya dates into European dates should have some way to set the so-called correlation number. Windows software *Maya Calendar Program Xoc Software DOS (Windows console applications) *Mayan Calendrics Hermetic Systems Web applications *Maya Calendar Dawn Jenkins & Michiel Berger *Pictographic Maya Calendar Converter C. Hartley *Calendar Converter John Walker *Yet Another Calender Converter Tim Forsythe *calendar conversion Tadayoshi Funaba (Haab, Tzolkin, Long Count) Meyer-Palmen Solilunar Calendar The Meyer-Palmen Solilunar Calendar has dates in the form cycle-year-month-day where each cycle consists of 60 years. Most years have twelve months, but some have thirteen. Windows software *Lunar Calendars and Eclipse Finder Hermetic Systems Miscellaneous calculators Web applications *Almagest Ephemeris Calculator Robert H. van Gent Ordinal (Day-in-Year) Dates Web applications *calendar conversion Tadayoshi Funaba Persian (Jalali) Calendar Web applications *Khayam Persian Calendar Program NetNative *Yet Another Calender Converter Tim Forsythe DOS (Windows console applications) *COMPUTUS Calendar conversion program Gerhard Behrens Solstices and Equinoxes Windows software *Equinox and Solstice Calculation Vernero Cifagni Web applications *Dates and Times of Equinoxes and Solstices Hermetic Systems *Seasons Institut de Mécanique Celeste et de Calcul des Ephemerides DOS (Windows console applications) *Dates and Times of Equinoxes and Solstices Hermetic Systems Symmetry454 Calendar Windows software *Kalendis Calendar Calculator Irv Bromberg Tabot Calendar The Tabot Calendar is a Rastafarian calendar related to the Common Era Calendar. Web applications Today's date in the Tabot Calendar Hermetic Systems Tibetan Calendar There is no Tibetan Calendar software at present which converts between Tibetan and Western dates because the exact calculational principles used by the Tibetan calendar makers from year to year has not been made public. There is, however, a web application for converting between Tibetan and Western years. Web applications *Tibetan Calendar Converter Fred Coulson Turkish Financial Calendar (Mali- or Rumi-Calendar) DOS (Windows console applications) *COMPUTUS Calendar conversion program Gerhard Behrens Vietnamese lunar calendar Web applications *Vietnamese lunar calendar Ho Ngoc Duc World Calendar (Achelis) Web applications *Yet Another Calender Converter Tim Forsythe Yerm Lunar Calendar The Yerm Lunar Calendar is a simple rule-based pure lunar calendar, which gains accuracy by allowing its lunar year (the yerm) to be much longer than a solar year. Web applications *Yet Another Calender Converter by Tim Forsythe converts the Yerm Lunar Calendar amongst others. Conversion is valid from 12 noon. The algorithm used is shown at Peter Meyer's web page. Zoroastrian Calendar Web applications *Zoroastrian Calendar NN